Unusual cerebrospinal fluid finding of intracytoplasmic granules in metaplastic carcinoma of the breast with acinar differentiation

Cerebrospinal fluid (CSF) evaluation for total and differential cell count is a common practice in pathology for evaluation of various disease conditions. Although rare, these CSF samples yield interesting and unusual morphological findings, which are not only of academic interest, but also may play key roles in diagnosis. For diagnosing metastatic carcinoma in brain and meninges, CSF examination is one of the important tools along with imaging studies. Metaplastic breast carcinoma (MBC) encompasses a rare (<1% of all breast cancers), aggressive and highly heterogeneous group of tumors. MBC is almost always estrogen receptor, progesterone receptor and Her2 negative (triple negative) and shows frequent early distant metastases as well as sub-optimal response to systemic therapies. The involvement of leptomeninges is most commonly associated with these triple- negative subtypes. In this report, we present an unusual case of malignant cells with prominent intracytoplasmic granules in CSF smears of a 46-year-old female with metastatic MBC with acinar differentiation. An extensive review of literature in English language did not return any other reports of a similar finding.